I've been through quite a few air grease guns and can't recomend a single one, including the brands and models listed already. They just don't hold up to daily use. I either have to spend the big money and get a commercial setup, or abandon the idea of an air grease gun. I'm hesitant on the battery units for the same reason. I question how long they will last if I use it every day?
My solution is to have two hand pump cheapy grease guns. There might be a better quality model out there, but I've found they all work about the same. I like the models with the handle that is held in place with the bracket, not the notch at the end. The bracket allows you to pull it out halfway if you want.
The reason I have more then one is to keep a flexible hose on one and a solid line on the other. The flexible line is good for tight spots, but it's terrible for anything else. Holding that stupid tube in place and pumping the grease gun takes three hands. With the solid tube, all you need is two hands. It's quick, easy and simple.
I've been using those two hand pumps for most of last year and will probably just keep on doing it this way. No more delays messing with airguns that quit working. No more pulling out the air hose. I just grab the gun, grease the fittings and get to work. Sometimes the simple way is the best way.
Eddie